How do i add material/textures to only one face of an object?
In Edit Mode select a face (using a face selection [Ctrl+Tab-->Face]) you want a texture to be projected on. Then press U-->Unwrap. In Uv Editor open your image texture.


Add a new material to your face (using a + button) and press the Assign button.


Then go to the Texture header. Add a new texture and change its type to Image or Movie. Open an image and change its coordinates (in a Mapping panel) to UV.


Result: